This calculator models the concrete as a cylinder around a round post. It subtracts the post cross-sectional area from the hole area, then multiplies by depth and the number of posts. Actual holes are rarely perfect cylinders, so treat the result as geometric volume before adding any project allowance.
Calculate
- Use the actual or planned hole diameter rather than a nominal auger label when possible.
- Post diameter must be smaller than hole diameter.
- The calculator does not determine required hole size, embedment depth, frost depth or structural adequacy.
- Local requirements, soil conditions and fence loading remain separate design decisions.
Concrete around a fence post
Hole volume minus the volume displaced by the post.
Fence-post concrete quantity: expose every geometric input
Post-hole concrete is simple only when hole geometry, post size and quantity are explicit. The data view keeps those inputs visible so users can spot the assumption that drives the result.
| Input | Why it matters | Verify |
|---|---|---|
| Hole diameter / width | Controls cross-sectional area | Actual excavation size |
| Concrete depth | Controls volume per hole | Planned concrete zone, not total post length |
| Post cross-section | May displace concrete depending on calculator mode | Actual post dimensions |
| Number of posts | Scales the total | Count corner/gate/special posts correctly |
| Package yield | Converts volume to bags | Exact product documentation |
How to use this page
Measure the project before entering values, keep units consistent, and review the assumptions shown with the result. The calculator is designed to expose the math it can perform and to stop before making a local-code, product-selection or professional-design decision it cannot support.
For irregular geometry, divide the project into simple sections, calculate each section separately and add the results. When a supplier, product label, plan set or project specification provides a value that differs from an example, use the project-specific value.
Sources
Sources support the scoped statements on this page; they do not imply local approval or product suitability.
Public corpus v1 · Method and scope reviewed for launch on 2026-08-13.
Estimate concrete around fence posts from hole geometry instead of using a bags-per-post guess
Fence-post concrete quantity depends on the actual hole dimensions, embedment depth and the space displaced by the post. A geometry-based estimate is more transparent than assuming every post uses the same number of bags.
Measure the hole, not just the post
The concrete occupies the space inside the hole that is not occupied by the embedded post. For a round hole and a round or approximately square post, the key inputs are hole diameter, post size and concrete depth.
If holes vary because of soil, auger drift or site conditions, use representative or individual measurements rather than assuming every excavation is identical.
Multiply one-post volume by the actual post count
Once the concrete volume around one post is known, multiply by the number of comparable holes. Different gate posts, corner posts or oversized footings should be calculated separately when their geometry differs.
Converting that total into bags requires the stated yield of the exact packaged mix. Bag size alone is not a sufficient yield assumption.
Depth and footing design are outside the calculator
The calculator should not choose embedment depth, frost protection, uplift resistance or lateral capacity. Those decisions can depend on fence height, wind, soil, local requirements and the fence system.
Use the tool after the project geometry has been determined, not as a substitute for that determination.
Verify before you use the result
- Measure the hole rather than assuming the auger nominal diameter.
- Confirm how the calculator handles post displacement.
- Read the bag yield from the exact mix being purchased.
Questions that come up before the next step
Why not just use a fixed number of bags per post?
Because hole diameter, depth and post displacement can change the concrete volume substantially. A geometry-based calculation makes those assumptions visible.
Does a larger post always mean more concrete?
Not necessarily. With the same hole size, a larger embedded post displaces more volume. In practice, larger posts may also use different hole geometry, so use the actual dimensions.
How do I convert the result to bags?
Use the total required concrete volume and divide by the stated yield of the exact packaged mix. Round up to whole bags and keep any project allowance explicit.
Primary and official references
Sources support the method and scope boundaries; project-specific requirements still need applicable product, supplier or local documentation.
Concrete yield as volume produced from a batch and the role of measured density.
Official ready-mixed concrete practice topics, including ordering and field quality topics.